This disclosure relates to continuous composite fiberglass rod for well pump drives and to apparatus and a method for attachment of end fittings to the rod.
During production of a well, for example an oil well, the pressure from the well reservoir often becomes insufficient to transport hydrocarbons to the surface without the assistance of a pump. In such cases, a downhole pump is typically lowered into the well, attached to the lower end of a sucker rod string. The upper end of the rod string is then attached to a pump jack or similar reciprocating surface apparatus. Through reciprocation of the pump jack, the rod string is used to drive the downhole pump, enabling continued production of the well.
Conventionally, sucker rods are formed from lengths of steel, typically about twenty-five (25) feet in length, which are connected to adjacent steel rods using cylindrical, metal end fittings. Steel is inherently heavy. A steel sucker rod requires sizeable equipment and a significant quantity of energy to reciprocate. Further, steel sucker rods weaken and eventually fail after substantial exposure to the corrosive environment within a well, causing steel sucker rods to frequently require replacement. Weakened and failed rods also often cause damage equipment and necessitating difficult and expensive removal operations. Additionally, the assembly of steel sucker rods and the repair of damaged steel sucker rods requires bulky equipment and precision welding, among other factors, which prevents the rapid and efficient construction and repair of steel sucker rods in the field.
To overcome the drawbacks relating to the use of steel sucker rods, fiberglass sucker rods were developed. Composite fiberglass rods provide sufficient strength to withstand axial loads similar to those of steel sucker rods while weighing considerably less. While a steel rod weighs approximately 2.9 pounds per foot when immersed in well fluid, a fiberglass rod of comparable length weighs only. 0.8 pounds per foot, resulting in a significant reduction in operational expenses relating to the energy required to reciprocate the rod. Lighter fiberglass rod segments are also easier and less expensive to transport, and easier and more efficient to handle and install. Additionally, fiberglass resists the corrosive effects of the well environment. Further, composite fiberglass rods exhibit improved flexibility and elasticity over steel rods, resulting a greater effectiveness per stroke of a pump jack.
A conventional fiberglass sucker rod string is formed from cylindrical fiberglass rod segments about 37.5 feet long and about 0.875 inches in diameter, each formed from bundles of glass filaments approximately 15 microns in diameter that have been wetted with a resin and formed into a rod via a pulltrusion process. Multiple round fiberglass rod segments are connected together using steel end fittings similar to those used to connect segments of steel rod, to form a multi-segment string of sufficient length to connect a pump jack and a downhole pump. To form the fiberglass sucker rod string, each rod segment must be individually connected to two end fittings, which are adapted to engage similar end fittings in adjacent rod segments. A curable adhesive, such as epoxy, is normally introduced into an end fitting, and a segment of fiberglass rod is then inserted. Once the adhesive cures, it binds to the fiberglass rod, forming a hardened plug that prevents removal of the rod from the end fitting during pumping operations.
U.S. Pat. No. 4,360,288, the entirety of the specification and drawings of which are incorporated herein by reference, describes a fiberglass sucker rod construction that includes a cylindrical fiberglass rod body having a steel fitting member adhesively bonded to each end thereof. The fitting members have internal receptacles with tapered annular spaces for receiving an epoxy to bond the fiberglass rod, forming wedge-like shapes of cured epoxy to prevent removal of the rod during operation.
U.S. Pat. No. 4,919,560, the entirety of the specification and drawings of which are incorporated herein by reference, describes an oil well sucker rod that includes a fiberglass rod with steel fittings on each end. An annular centering surface and a plurality of dimples within the fitting serve to center the rod at two points within the fitting, while taper angles of the interior tapered surfaces decrease progressively toward the open end of the fitting.
U.S. Pat. No. 6,193,431, the entirety of the specification and drawings of which are incorporated herein by reference, describes a fitting for connecting rods, and a sucker rod construction using the fitting. The interior cavity surface of the fitting is shaped to form one or more annuluses between the inserted rod and the fitting to form axially aligned wedges having a wide portion that narrows toward the open end of the cavity and approaches the rod, asymptotically.
Application for U.S. patent Ser. No. 11/715,085, filed Mar. 5, 2007, describes a continuous non-round composite fiberglass sucker rod connected within a metal fitting using a curable adhesive. The fitting includes a rod interior cavity or receptacle shaped to form one or more tapered cylindrical wedges having a wide portion that narrows toward the open end of the fitting. The cavity contains the adhesive and the end of the rod.
The advantages of a sucker rod string formed from multiple segments of fiberglass rod over a conventional steel sucker rod are numerous. However, a continuous fiberglass rod that extends from the surface of a well to the downhole pump with no interconnections or joints therebetween thereby requiring only the single connection at each end to connect the pump jack to the downhole pump is even more advantageous. A continuous fiberglass rod is significantly easier and less expensive to store, handle, transport, and install by eliminating the time, materials, space, and labor required to create a large number of interconnections between each rod segment.
Early attempts to create continuous composite fiberglass rods encountered numerous difficulties and failures. While fiberglass rod is able to withstand a significant axial load, equal to that of a steel rod, early fiberglass rods, known as ribbon rods, readily cracked or broke if twisted, or bent beyond tolerance. Thus, when attempting to coil a continuous fiberglass ribbon rod about a spool, an impractically large spool is required to avoid coiling the rod beyond its tolerance. With ribbon rod, normally stored on a spool in a single wrap as illustrated in U.S. Pat. No. 4,563,391, a very limited amount of fiberglass ribbon rod could be spooled. The weight of exterior layers of rod on the spool cracks interior layers.
Existing fiberglass sucker rod systems employ rod having a generally cylindrical rod, with a round cross section. However, it has been determined that the ability of a fiberglass rod to withstand the axial loads inherent in downhole pumping operations depends primarily on the cross sectional area of the rod, rather than the shape of the rod. Thus, it is possible to create a composite fiberglass rod having a non-round cross section, thereby having different bending moments of inertia in different bending directions, depending upon the cross-sectional shape of the rod, enabling a composite fiberglass rod having a suitable cross-sectional shape to be coiled about a spool without damaging the rod, to withstand the weight of exterior layers of rod on the spool without cracking, and to withstand the weight of a dispensed portion of the rod on the spooled portion of the rod without breaking.
For example, a conventional fiberglass sucker rod, having a round cross section, would have an bending moment of inertia in any direction. A round fiberglass rod approximately 0.5 inches in diameter would require a spool eight feet in diameter to coil the rod without causing damage, Conversely, a composite fiberglass rod having a rectangular cross-section that is 0.375 inches by 1.75 inches could be successfully coiled on a spool as small as forty eight inches (48″) in diameter.
Conventional end fittings or fittings are designed to accommodate cylindrical rods, having a generally round cross section. To date, no method or system exists for creating sucker rod constructions, or similar assemblies, from non-round composite fiberglass rods and/or repairing composite fiberglass rods having a non-round cross section utilizing conventional end fittings.
Conventional systems and methods for assembling and repairing sucker rod assemblies require cumbersome and bulky equipment, thereby restricting the creation and/or repair of sucker rods to designated locations configured for such a purpose. To date, no portable method or system exists for creating sucker rod constructions from composite fiberglass rods and/or repairing composite fiberglass rods in the field.
A need exists for a method usable to create a composite fiberglass rod having a non-round cross section, thereby exhibiting improved flexibility, and storage ability, while retaining an equal or greater axial strength than a comparable round rod.
A need also exists for a method for forming a composite fiberglass rod having a non-round cross section suitable for the formation of a continuous fiberglass rod, lacking any intermediate fittings or joints, thereby conserving the time and labor relating to assembly of sucker rod rings.
Use of such a non-round composite fiberglass rod would enable a continuous composite fiberglass rod to be constructed, extending from the surface of a well to the downhole pump with no interconnections or points therebetween, thereby requiring only the single fitting at each end to connect the pump jack to the downhole pump. Continuous fiberglass rods would be significantly easier and less expensive to store, handle, transport, and install, compared to noon-continuous rods, and would eliminate the time, materials, space, and labor required to create a large number of interconnections between each rod segment. Further, a large quantity of continuous composite fiberglass rod can be wrapped around a spool for facilitating storage and installation, due to the improved bending radius of the non-round composite fiberglass rod.
A need exists for a composite fiberglass rod usable to actuate a downhole pump, having a non-round cross section, thereby exhibiting improved flexibility, and storage ability, while retaining an equal or greater axial strength than a comparable round rod.
A need also exists for a composite fiberglass rod having a non-round cross section, suitable for the formation of a continuous fiberglass rod, lacking any intermediate fittings or joints, thereby conserving the time and labor relating to assembly of sucker rod strings.
A need also exists for a composite fiberglass rod having a non-round cross section that is usable with conventional sucker rod systems and fittings including the conventional steel end fittings, as well as other types of fittings and system components.
A need also exists for a system and method that can evenly heat a quantity of curable adhesive, at a uniform and controlled temperature, to efficient provide an effective connection between a fiberglass rod and an end fitting.
A need exists for a portable system and method that is usable in the field to quickly and efficiently secure an end fitting to a composite fiberglass rod using a curable adhesive.
A further need exists for a system and method that can secure an end fitting to a composite fiberglass rod when the end fitting has a cross sectional shape different from that of the rod.
The present embodiments meet these needs.